This invention relates to a process for the isolation of component materials of aqueous solutions soluble in lipophilic solvents and to the use of certain concentration agents for the carrying out of the process.
The extraction of such lipophilic solvent-soluble component materials is of increasing importance, especially in diagnosis, where the detection or determination of component materials of body fluids is already carried out to a great extent. In these biological and medicinal investigations, as a rule the component materials to be determined are extracted from the aqueous liquids with the aid of lipophilic solvents. These component materials are thereby separated and thus purified from undesired accompanying materials, e.g., sugars, salts, proteins, urea, frequently present in large excess. By concentration of the thus-obtained extracts, component materials present only in small amounts can also be enriched. In some cases, they are accessible to analytical methods only in this way.
However, the methods previously available are not satisfactory and exhibit considerable disadvantages, especially in the case of extraction of component materials from body fluids, such as urine, blood, serum or extracts or parts of organs or tissues.
In the case of a direct extraction of the aqueous phases with lipophilic solvents, as is known from experience, phase separation is very difficult to carry out since emulsions are frequently formed which cannot be separated or can only be separated with difficulty and thus make a quantitative extraction impossible. Furthermore, the breaking of the emulsions necessitates an additional expenditure of time, which is disadvantageous, especially in the case of serial investigations.
It has previously been attempted to achieve an isolation of these component materials by their absorption from the aqueous solution by a concentration agent. For this purpose, numerous materials have been suggested, e.g., anhydrous sodium and magnesium sulphate, adsorbents based on silicate, such as conventional silica gel or florisil, molecular sieves and ionic cellulose ethers. These concentration agents admittedly possess high water retention capacities but from their mixtures with body fluids, the component materials to be determined cannot be quantitatively extracted due to inclusions, irreversible adsorptions or ion exchange processes. Particularly, the previously employed silicate surface active adsorbents possess the disadvantage that a desorption of the component materials to be investigated is not possible quantitatively with the help of lipophilic solvents as a result of the activity or polarity of the surface of these adsorbents. Polar compounds such as, morphine, may not even be extracted by mixtures of lipophilic and polar solvents without simultaneous desorption of the water.
This applies, e.g., also to the process, described in Clinical Chemistry, pages 593 to 596, 1973, for the determination of organic acids in the urine. This process employs a selective extraction by an adsorption and partition chromatography with one of the activated silica gels usually employed therefor.
The silica gel employed possessed a particle size of 0.05 to 0.2 mm. but the described process shows that, due to the properties of this material, the polar component materials are held back by the silica gel. The non-polar substances are also relatively strongly adsorbed and then only slowly liberated again. This follows, inter alia, from the amounts of solvent necessary for the extraction and their composition of polar and non-polar solvents. Thus, e.g., for 1 part by volume of sample liquid, there are used about 25 parts by volume of solvent. Thus, the silica gel possesses too high an activity. Furthermore, according to this previously known process, a mechanical mixing of the sample liquid with the silica gel is necessary. However, in the case of a subsequent quantitative determination, this is a further source of error. If one attempts to employ the method indicated by way of example for fatty acids for the extraction of pharmaceuticals or of their metabolites with the conventional silica gel, the method does not work. The metabolites and their parent substances of various structure are even adsorbed from the aqueous solution. A desorption only takes place with polar solvents and then with the co-extraction of the water. However, in this way, the desired object of carrying out a purification and concentration of the component materials cannot be achieved.
According to this invention, the disadvantages of the known processes are overcome and a process is made available by which a gentle and quantitative extraction of component materials of aqueous solutions soluble in lipophilic solvents is possible.
It has been found that certain concentrating agents are able to take up the aqueous solutions with the maintenance of their flowability and that the component materials can be obtained quantitatively from these mixtures and surprisingly with very small amounts of solvent. This method is extremely gentle so that neither the aqueous liquids nor the component materials are changed by this treatment. The take up of the aqueous solutions takes place quantitatively since the amount of the concentrating agent is so adjusted that at most the maximum water take up capacity is reached. The subsequent desorption of the component materials from the flowable, charged concentrating agent with lipophilic solvents takes place without problems and quantitatively.